1. Field of the Invention
The present invention generally relates to a control technique of a magnetic disk storage apparatus. More specifically, the present invention is directed to a control technique of a voice coil motor capable of moving a magnetic head for reading/writing information with respect to a storage track formed on a magnetic storage disk to be rotatably driven.
2. Description of the Related Art
A magnetic disk storage apparatus is provided with a magnetic head, a voice coil motor, and a voice coil motor drive control circuit. The magnetic head reads/writes information with respect to storage tracks formed on a magnetic storage disk which is rotatably driven in a high speed. The voice coil motor moves this magnetic head on the magnetic storage disk in both a seek move manner and a tracking move manner. The voice coil motor drive control circuit controls a drive current of the voice coil motor, while monitoring a read condition of the magnetic head, in order to perform a positioning operation of the magnetic head.
While information storage density of magnetic disk storage apparatus is increased year after year, highly precise positioning control operations of magnetic heads are required in connection with this high storage density requirement. Under such a circumstance, the positioning system of the magnetic head has been employed in which the drive current of the above-described voice coil motor is feedback-controlled based upon the detected value of this drive current. Then, generally speaking, in order to drive the voice coil motor for moving this magnetic head, such a liner drive system has been employed in which the drive current amount of the voice coil motor is changed in the continuous manner.
The above-described conventional techniques own the below-mentioned problems which could be revealed by the Inventors of the present invention.
That is, in a magnetic disk storage apparatus, high density storage operation is required and also, highspeed across operation is required. In order to realize such highspeed access operation, time during which a magnetic head is moved to a predetermined storage track of a magnetic disk, namely, so-called xe2x80x9cseek timexe2x80x9d should be shortened. To reduce the seek time, a drive current of a voice coil motor should be increased. However, when the drive current of the voice coil motor is increased, power loss required to control this motor drive current in the linear manner is increased, resulting in an increase of a heat generation amount. This heat generation occurred during the seek operation may give adverse influences to operations and characteristics of the magnetic head and the magnetic storage disk. As a result, for instance, there is such a problem that read/write errors may be easily produced.
To reduce the above-explained heat generation, the Inventors of the present invention have studied that the above-described drive current of the voice coil motor is controlled in the pulse width modulation control manner (will be referred to as a xe2x80x9cPWM controlxe2x80x9d hereinafter). In other words, the Inventors of the present invention have investigated such a pulse drive system. That is, while the drive current amount of the voice coil motor is not continuously changed, a ratio of turn-ON time to turn-OFF time of this drive current (namely, so-called xe2x80x9cduty ratioxe2x80x9d) is changed to execute the drive control of the voice coil motor. In this case, the drive control operation of the voice coil motor is carried out in such a manner that while the drive current amount of the voice coil motor is fixed to a value approximated to the maximum value, this ratio of the turn-ON to the turn-OFF of the drive current is changed. This drive system corresponds to one sort of switching control operation, and can achieve a very large effect as to the reduction of the power loss.
However, although this pulse drive system can have a merit as to the suppression of the heat generation amount by reducing the power loss, this pulse drive system can hardly realize high control precision, as compared with that of the above-explained linear drive system. In particular, this pulse drive system can hardly secure sufficiently high positioning precision of the magnetic head during the tracking operation in which the move amount of the magnetic head is small.
Under such a circumstance, the Inventors of the present invention has considered that when the large drive current of the voice coil motor is required so as to move the magnetic head in the seek mode and in highspeeds, the drive operation by the PWM control manner (namely, pulse drive mode) is carried out, whereas when the high precision drive control is required so as to perform the tracking control while the amplitude of the drive current is small, the drive operation by the linear control (namely, linear drive mode) is carried out. In this case, when the pulse drive operation and the linear drive operation are carried out by separately employing output amplifiers, the arrangement of the magnetic disk storage apparatus becomes complex and is manufactured in a large scale. In particular, the switching operation between the voice coil motor and the output amplifiers becomes very complex and very cumbersome. In order that the arrangement is not made complex, or in the large scale, the following manner is rational, namely, both the pulse drive operation and the linear drive operation may be commonly executed by the same output circuit.
In other words, the output amplifier which supplies the drive current to the voice coil motor is commonly used during both the pulse drive operation and the linear drive operation. To this end, the output amplifier is arranged in such a manner that the input of this output amplifier is used to switch the pulse drive mode and the linear drive mode in response to a magnitude of a control amount. When the pulse drive operation is carried out, the PWM-controlled pulse signal is entered to the output amplifier. In this case, this PWM-controlled pulse signal owns a sufficiently large amplitude in such a manner that the output amplifier may be fully operated over the dynamic range thereof. As a consequence, while the output amplifier is operated over the full dynamic range under which the output signal of this output amplifier becomes saturated, this output amplifier may supply the pulse drive current to the voice coil motor.
When the linear drive operation is carried out, since such an input signal whose level is changed in a linear mode in response to a change contained in control amounts is entered into the above-explained output amplifier, the voice coil motor is driven in the linear drive mode. In this case, this input signal corresponds to such a signal having a small amplitude which can be fully stored within the dynamic range of the output amplifier. More specifically, when the tracking operation is carried out during which the position of the magnetic head is controlled in the very precise manner, the output amplifier supplies a drive current to the voice coil motor under such a condition approximated to a zero level output.
As explained above, the output amplifier may be commonly used during both the pulse drive operation and the linear drive operation. As a consequence, while the construction of the magnetic disk storage apparatus is not made complex and in the large scale, the voice coil motor can be driven in accordance with such a drive system (namely, either pulse drive system or linear drive system) which is suitably selected during either the seek operation or the tracking operation.
However, it can be recognized that the above-described hybrid drive system of the pulse/linear drive modes own the following problems.
That is, in order that the PWM drive operation is effectively carried out, such an output amplifier operable with a large amplitude and in a high slew rate is necessarily required. In the pulse drive system, the electric power loss can be reduced by controlling the drive current in the high speed by way of the switching control manner. However, when the slew rate is low, the power loss (switching loss) occurred during the switching control operation is increased, so that the merits achieved by this pulse drive system are deteriorated. Although such an excessively high slew rate may probably increase the occurrence of EMI noise, a higher slew rate than a predetermined slew rate is required so as to achieve the originally achieved merits of the pulse drive system.
To drive a voice coil motor, such an amplifier should be used, while this amplifier is operable with both a source output for pushing out a current and a sink output for pulling a current. As an amplifier capable of performing such an output operation, a so-called xe2x80x9cpush-pull type output circuitxe2x80x9d is used. In this push-pull type output circuit, an output element used to control a current pushing amount (either source or push current) is series-connected to another output element used to control a current pulling amount (either sink or pull current), namely a longitudinal connection. A push-pull type output circuit is constructed in such a manner that a push-driving (source) output transistor is series-connected to a pull-driving (sink) output transistor between a positive side and a negative side of a power supply, and an output signal is derived from an intermediate connection point (node) of these transistors.
In the above-described push-pull type output amplifier, a pass-through current (penetration current) problem may occur, while this pass-through current passes through a push-sided transistor to a pull-sided transistor. When this pass-through current is increased, useless power consumption which does not contribute the output signal is increased. Also, when an excessively large pass-through current flows from the push-side transistor to the pull-side transistor, the output transistor may be destroyed. As a result, it is desirable that the pass-through current should be made small as being permitted as possible. In such an output amplifier operated in a B-class mode, since such a operation condition is set, this pass-through current may be interrupted, or cut off, while any one of a push-sided transistor and a pull-sided transistor should be brought into an OFF state in this operation condition.
However, on the other hand, in order to achieve a better linear characteristic, such a passthrough current having a certain value should be supplied. In a B-class amplifier, in the vicinity of an output zero point, namely a so-called xe2x80x9czero-cross pointxe2x80x9d, a so-termed xe2x80x9cswitching noisexe2x80x9d may be produced when one of both a push-sided transistor and a pull-sided transistor is switched from an ON state into an OFF state, and also the other transistor is switched from an OFF state into an ON state. In the case that a voice coil motor is driven in a linear drive mode, the switching noise produced in the vicinity of the output zero point may deteriorate both control precision and stable characteristics of tracking control operation which is carried out in the vicinity of this output zero point.
As previously explained, on the other hand, in such a case that the voice coil motor is driven in the pulse drive mode, such an output amplifier having a large amplitude and operable in a high slew rate is required. However, in such an output amplifier operable in a high slew rate, a pass-through current very easily flows. More specifically, in such an output amplifier operated over a full range in a switching mode, when both a push-sided transistor and a pull-sided transistor are simultaneously brought into ON states even in very short time, an extremely large pass-through current will flow at an instance when both the push/pull transistors are turned ON at the same time. In the worst case, these push/pull transistors and/or a power supply may be brought into break-down conditions. Even when such a break-down condition does not occur, large transition noise which may cause EMI noise is produced. Since this pass-through current may cause such a problem that power consumption is increased even when the voice coil motor is driven in the linear drive mode, it is preferable to avoid that this pass-through current becomes excessively large.
As previously explained, it is desirable to drive the voice coil motor with the large amplitude and in the high slew rate in the pulse drive operation. However, there is such a contradictory aspect that when this slew rate becomes excessively high, EMI noise is increased. On the other hand, when the slew rate is low, there is another problem that power consumption caused by switching loss is increased. Also, in the case that the voice coil motor is driven in the pulse drive mode, even if a control current is slightly deviated, then a pass-through current may flow through the output transistor. As a result, a care should be taken into such an aspect that the power consumption is increased by this pass-through current.
As to other aspects, since a large current may flow through an output transistor, such an electronic element having a large size is employed, as compared with a size of an internal electronic element. Also, an externally-mounted electronic element may be employed as the output transistor. As explained above, when the size ratio of the output transistor to the internal electronic element is large, a difference between the characteristics of these electronic elements due to manufacturing fluctuations is increased. In particular, in such a case that an externally-mounted electronic element is employed, since a manufacturing process of this externally-mounted electronic element is different from that of the internal electronic element, a difference between the characteristic of this externally-mounted electronic element and the characteristic of the internal electronic element which drives this externally-mounted electronic element is further increased.
As a consequence, in such a case that the above-described idling current is supplied in order to improve the linear characteristic of the output current during the linear drive operation, the following problems may occur. That is, the fluctuation of this idling current is increased due to this difference between the characteristics of these electronic elements. Thus, the power consumption becomes excessively larger than the expected power consumption, so that heat generations are increased. Although the power consumption is small, the switching noise is increased. As a result, such an optimum operation cannot be achieved, while this optimum operation is required so as to drive the voice coil motor in the high precision manner.
As previously described, the following fact can be revealed. That is, in the magnetic disk storage apparatus, the hybrid drive system may expect such a large merit as to the power consumption and the control precision, but may cause the above-explained various contradictory problems in such a case that both the pulse drive operation and the linear drive operation are commonly carried out by employing the same output amplifier. In this hybrid drive system, the voice coil motor for moving the magnetic head in either the seek mode or the tracking mode is driven by switching the pulse drive operation and the linear drive operation in response to the magnitude of this head drive amount.
The present invention has been made to solve the above-described problems of the conventional hybrid drive system, and therefore, has an object to provide such a technique capable of driving a voice coil motor by switching a drive mode thereof as either a pulse drive mode or a linear drive mode in response to a magnitude of a drive amount of this voice coil motor which moves a magnetic head in either a seek mode or a tracking mode, and also capable of performing both the pulse drive mode and the linear drive mode under optimum conditions by employing the same output amplifier.
Furthermore, another object of the present invention is to provide such a technique capable of realizing such operations that since the voice coil motor is driven with a high amplitude and in a high slew rate during the pulse drive mode, access operation of the magnetic head can be carried out in a high speed by shortening seek time. Also, this technique can realize such operations that while both an occurrence of EMI noise and a heat generation which may probably induce read/write errors are suppressed to minimum values during the linear drive mode, a positioning control operation of the magnetic head can be carried out in high precision during the tracking operation.
The above-described objects and other objects as well as features of the present invention may be understood from detailed descriptions of the specification and also accompanying drawings.
A typical inventive idea of the present invention selected from the disclosed present inventive ideas will now be briefly explained as follows:
That is, in such a magnetic disk storage apparatus that a magnetic head for reading and/or writing information with respect to storage tracks formed on a magnetic storage disk to be rotatably driven is driven by a voice coil motor, a magnetic head drive control means for executing a positioning control operation of the magnetic head by feedback-controlling a drive current of the magnetic head while monitoring a read condition of the magnetic head is provided with a linear drive mode under which the voice coil motor is driven in a linear control manner, and a pulse drive mode under which the voice coil motor is driven in a pulse width control manner. When a drive current of the voice coil motor is small, the magnetic head drive control means executes the linear drive mode, whereas when a drive current of the voice coil motor is large, the magnetic head drive control means executes the pulse drive mode. Both the linear drive mode and the pulse drive mode are carried out by employing a commonly-used output amplifier. The commonly-used output amplifier is arranged as a push-pull type output circuit made of both a push-driving output transistor and a pull-driving output transistor. Also, an operation mode of this output amplifier is set to an AB-class operation during the linear drive mode, whereas the operation mode of this output amplifier is set to a B-class operation during the pulse drive mode.
In accordance with the above-described magnetic head drive control means, the voice coil motor can be driven by switching the drive mode thereof as either the pulse drive mode or the linear drive mode in response to the magnitude of the drive amount of this voice coil motor which moves the magnetic head in either the seek mode or the tracking mode, and also both the pulse drive mode and the linear drive mode can be carried out under optimum conditions by employing the same output amplifier. As a consequence, the voice coil motor can be driven by using the drive system (pulse/linear drive systems) suitable for the seek operation and the tracking operation, respectively.
Also, in the above-described magnetic disk storage apparatus, even in such a case that the voice coil motor is driven in the low slew rate during the linear drive mode, or in the high slew rate during the pulse drive mode, the voice coil motor used to move the magnetic head in either the seek operation or the tracking operation can be driven in response to the magnitude of this drive amount by switching the pulse drive mode, or the linear drive mode, and furthermore, both the pulse drive operation and the linear drive operation can be carried out by employing the same output amplifier under better conditions.
As a consequence, while the construction of this magnetic disk storage apparatus is not made complex and in a large scale, the seek time is shorten, so that the access operation of the magnetic head can be carried out in high speeds. On the other hand, during the linear drive mode, while both the generation of the EMI noise and the heat generation which may probably induce the read/write errors are suppressed to the minimum values, the magnetic head positioning control operation can be carried out in the high precision during the tracking operation.